Moving picture coding apparatus and moving picture decoding apparatus

Abstract

A video encoder ( 70 ) for coding moving pictures comprising a buffer ( 16 c ) with a plurality of memory areas capable of storing frames composed of top fields and bottom fields, a motion estimation unit ( 19 ) operable to code, field by field, inputted pictures performing moving estimation and moving compensation by referring, field by field, to the picture data stored in a memory area, a motion compensation unit ( 16 d ), a subtractor ( 11 ), a transformation unit ( 13 ) and a quantization unit ( 14 ), a memory management unit ( 71 ) operable to manage, frame by frame, a plurality of memory areas, an inverse quantization unit ( 16 a ) and inverse discrete cosine transform unit ( 16 b ) operable to decode picture data in coded fields and store the picture data in the decoded field in any of the plurality of memory areas under the management by the memory management unit ( 71 ).

The invention claimed is: 
     
       1. A picture coding and decoding system comprising:
 a picture coding apparatus which codes a sequence of pictures in a moving picture; and 
 a picture decoding apparatus which decodes the sequence of coded pictures in the moving picture, 
 wherein said picture coding apparatus includes: 
 a first memory having a plurality of memory areas, each memory area being capable of storing picture data of a field, or a frame comprising one top field and one bottom field; and 
 a coding unit configured to code the sequence of pictures in the moving picture on a field by field basis, and 
 wherein said picture decoding apparatus includes: 
 a second memory having a plurality of memory areas, each memory area being capable of storing picture data of a field, or a frame comprising one top field and one bottom field; 
 a decoding unit configured to decode the sequence of coded picture on a field by field basis, by referring to a reference field stored in one memory area; 
 a memory management unit configured to manage each memory area on a frame by frame basis; and 
 a storing unit configured to store a decoded field decoded by the decoding unit into one memory area included in the plurality of memory areas under management of the memory management unit, 
 wherein said memory management unit is further configured to: 
 (1) set a state corresponding to one memory area to be “used” when a frame comprising one top field and one bottom field, a top field, or a bottom field, any of which is to be referred to when decoding another field, is stored in the one memory area; and 
 (2) set a state corresponding to one memory area to be “unused” when (i) no picture data is stored in the one memory area, (ii) a frame stored in the one memory area is unused for reference, and (iii) both of a top field and a bottom field stored in the one memory area are unused for reference, and 
 wherein said memory management unit is further configured to: 
 when a first field is a reference field and the first field which is a top field or a bottom field is stored in the one memory area for which a state is “unused” and the state corresponding to the one memory area is set to be “used”, 
 (1) allow a second field to be stored in the one memory area in the case where the second field is a reference field and the second field is a bottom field or a top field of a same frame; and 
 (2) prohibit a second field from being stored in the one memory area into which the first field is stored and allow the second field to be stored in another memory area other than the one memory area and included in the plurality of memory areas in the case where the second field is a reference field but the first field and the second field do not constitute a same frame.